East Texas Quarterly Magazine Summer 2015 | Page 7

downward trend is encouraging, shooting mortality could
still be a limiting factor, particularly in remote areas.

of prey fed on these animals, they accumulated DDE in
their systems.

Human disturbance can also be a cause of population
decline. Activities such as logging, oil exploration and
extraction, construction, and recreational activity
certainly do disturb eagles in some instances. However, the
impact of these disturbances is highly variable, depending
on the activity, its frequency and duration, its proximity
to areas used by eagles, the extent to which the activity
modifies the habitat or its use, and timing in relation to the
reproductive cycle. Also, some birds are more tolerant
of disturbance than others, with adults generally less
tolerant than immature birds. Despite this variability,
disturbance near nests have caused nesting failures.

Although occasionally causing death, DDE mainly
affected reproduction. Some birds affected by the
chemical failed to lay eggs, and many produced thin
eggshells that broke during incubation. Eggs that did not
break were often addled or contained dead embryos, and
the young that hatched often died. Dieldren killed eagles
directly rather than causing thin eggshells, but compared
to DDT, Dieldren was probably not as important in overall
Bald Eagle declines. In 1972, the EPA banned the use of
DDT in the United States. Since the ban, DDE residues in
Bald Eagle eggshells have dropped significantly, and a slow
recovery of eagle productivity has occurred. Most
populations appear to be producing chicks at the
expected rate.

Finally, the most dramatic declines in Bald Eagle
populations nationwide resulted from environmental
contaminants. Beginning in 1947, reproductive success in
many areas of the country declined sharply, and remained
at very low levels through the early 1970’s. After several
years of study, the low reproduc ѥ